Add PolicyKit action to leafpad package

[apt-ghetto]

The package gksu has been removed from 18.04 and sudo should not be used to start a graphical application, because of problems caused by environment variables (e.g. $HOME, $XAUTHORITY) not set in the right way.

Please add a PolicyKit action to the package, so that you can edit for example the /etc/fstab configuration file by typing: pkexec leafpad /etc/fstab

I suggest to add the file /usr/share/polkit-1/actions/com.ubuntu.pkexec.leafpad.policy with the content like:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policyconfig PUBLIC
 "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/PolicyKit/1/policyconfig.dtd">
<policyconfig>

  <action id="com.ubuntu.pkexec.leafpad">
    <message>Authentication is required to run the Leafpad Editor</message>
    <icon_name>leafpad</icon_name>
    <defaults>
      <allow_any>auth_admin</allow_any>
      <allow_inactive>auth_admin</allow_inactive>
      <allow_active>auth_admin</allow_active>
    </defaults>
    <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/leafpad</annotate>
    <annotate key="org.freedesktop.policykit.exec.allow_gui">true</annotate>
  </action>

</policyconfig>

[apt-ghetto (apt-ghetto)]

The support for Lubuntu 18.04 ended